RSS Ajax JavaScript ticker

In this tutorial,
I'll show you how to combine RSS, Ajax, and JavaScript to create a live RSS ticker.
Thanks to Ajax, the conventional roles of server side and client side
programming are reversed in an application like this as JavaScript- not PHP- is
used to handle much of the work, including parsing the RSS file.

I've learned it's good form to always show your viewers exactly where you're leading them to
begin with,
so here are a couple of examples of the Ajax style RSS ticker I'll be discussing
how to create:

A very simple PHP script is used to get the contents of an RSS file
online and save it locally on the server for caching, unparsed in any way.

Ajax is used to fetch the contents of the RSS file produced by the PHP
script.

JavaScript receives the contents of this RSS file (via
Ajax), then parses it using standard DOM methods before displaying the feed in any
manner the webmaster desires.

As you can see, the server side script, PHP in this case, does very little of
the work. The majority of the workload is shifted to the client
side, including much of the interface for customizing the ticker, such as the amount of
time to cache the RSS file etc. It's arguably more efficient than using PHP to
do all the parsing, though the main attraction for me is that I get to be in
familiar territory much of the time, basked in JavaScript.

Ok, so lets get started! First stop, creating a PHP script for fetching the
contents of a file online.